1. Field of the Invention
This invention relates to a vibration isolating bushing mainly used, being built-in in a suspension system of an automobile, etc.
2. Description of the Related Art
Hitherto in an automobile suspension system, vibration isolating bushings have been used for the purposes of vibration damping and shock absorbing at connecting parts of the vehicle body and the suspension, namely, each connecting part between a support member such as a control arm carrying wheels, etc. and a body side member such as body frame and the like. It is also known that a tubular vibration isolating bushing has been used as an engine mount.
In FIG. 3 is shown one example of a conventional vibration-proof bushing 20 in cross-sectional view. The vibration-proof bushing 20 is made up of an inner cylinder 22 and an outer cylinder 23 made of a metal and disposed concentrically, and a rubber elastomer 24 interposed between the inner and outer cylinders 22, 23.
As for the aforesaid inner cylinder 22, an inner cylinder assuming a straight form was generally employed in the past, but at terminal edges of such straight cylinder in the state of use each constituting a contact surface with another member, their surface pressures were high. Recently with a view to inhibiting such high surface pressures at the terminal edges of inner cylinder during use, an approach of upsetting extremities of the inner cylinder 2 has been being adopted thereby to enlarge the areas of the edges as illustrated in FIG. 3. In that case, in order to enlarge the areas of extremities of the rubber elastomer 24 between the inner and outer cylinders and to secure sufficiently a free length from elastic deformation, it was further proposed to perform the upsetting forming by subjecting extremities of the inner cylinder 22 to plastic working such as ironing working after vulcanization forming (JP Registered Patent No. 2723424). The reference numeral 25 designates the upset portion.
The vibration-proof bushing 20 is used in the state that the inner cylinder 22 inserts therein a shaft member 11 as one support member to be fastened to a member 12 on the vehicle body side, such as body frame whereas the outer cylinder 23 is press fitted and secured into a hole 14 for attachment of the other support member 13 such as a wheel-supporting arm. In this press fitting of the outer cylinder 23, formerly as illustrated in FIG. 3, in order that forcing or push-in may be performed by the use of a jig for press fitting, its axially one extremity was once upset radially outwardly and then bent radially inwardly into an inward bend form thereby to secure a forcing allowance for the jig. However, a problem encountered when the vibration-proof bushing 20 was press-fitted in the attachment hole 14 of the support member 13 was that the press-fit jig for forcing or urging the outer cylinder 23 was prone to slip at the inward bend portion 26, so that it was difficult to force the jig with the result that workability was reduced.
Further, as is the case with FIG. 3, in case where the vibration-proof bushing 20 was used with its axis center oriented vertically (up-and-down direction) and with the support member 13 on the arm side, which press fits fixedly the outer cylinder 23, suspended and supported to the body side member 11, if the rubber elastomer 24 between the inner and outer cylinders 22,23 was separated or ruptured, there was a risk of the outer cylinder 23 releasing or falling off from the inner cylinder 22. The case was also true when the bushing 20 was likewise used with its axis center oriented horizontally.
In view of the aforementioned problems or difficulties, this invention has been accomplished and provides a vibration isolating bushing constructed so that a forcing allowance sufficient to press fit the outer cylinder to a support member can be secured and accordingly, the workability in assembling work can be improved, and even if a rupture occurs at the rubber elastomer, the release, detachment or falling of the outer cylinder from the inner cylinder can be avoided.
This invention resides in a vibration isolating bushing comprising an inner cylinder, an outer cylinder disposed outwards of it to be spaced apart, and a rubber elastomer interposed between and interconnecting the inner and outer cylinders by vulcanization forming, which bushing is characterized in that the inner cylinder is subjected to upsetting forming at its axial extremities outwardly, thus forming upset portions, the outer cylinder is formed, at its one axial extremity, with a flange portion, the flange portion having a larger diameter than an outside diameter of the upset portion; the one axial extremity of the outer cylinder has an inside diameter which is made smaller than the outside diameter of the upset portion.
According to the vibration isolating bushing of the invention, when press-fitted to an attachment hole of a member to be assembled, it is possible to abut the top end of a press-fit jig securely on the flange portion of the outer cylinder at its extremity and accordingly, to force and press fit the bushing securely without any risk of causing slipping or disengagement of the jig. Thus the workability in assembling the vibration isolating bushing can be enhanced.
Furthermore on account of the construction that the inside diameter of the flange portion of the outer cylinder at its one extremity is made smaller than the outside diameter of the upset portion of the inner cylinder at its extremity, even if a rupture or the like occurs at the rubber elastomer between the inner and outer cylinders and as a result, the outer cylinder is released or falls off from the inner cylinder, the smaller-diameter portion of the outer cylinder at the extremity is able to abut on the upset portion at the extremity of the inner cylinder, thus impeding further release or detachment. As a consequence, when using in a manner that the arm side support member, into which the outer cylinder is press-fitted and fixed with its axial center oriented vertically, is supported to the body side member to which the inner cylinder is secured in a suspended manner, it is possible to obviate the risk of the outer cylinder being detached and coming off from the inner cylinder even if a rupture or the like occurs at the rubber elastomer.
In the vibration-isolating bushing as described above, it is preferred that the one axial extremity on the flange portion side of the outer cylinder be slightly diminished in diameter so that its inside diameter is smaller than the outside diameter of the upset portion at the extremity of the inner cylinder. The process of upsetting forming the extremity of the inner cylinder, for example, by plastic working, etc. has its own limits in upsetting degree. Therefore the one extremity of the outer cylinder is diminished in diameter as mentioned above simultaneously when forming the flange portion by drawing working, etc., whereby it is easily possible to make the inside diameter of the outer cylinder at the extremity smaller than the outside diameter of the upset portion of the inner cylinder at its extremity.
It is preferably after vulcanization forming that the terminal upset portion of the inner cylinder is formed by plastic working so as to enlarge its edge surface. Thus it is possible to make the area of the terminal surface of the rubber elastomer larger and to secure sufficiently a free length to the elastic deformation, thereby improving its durability.